Data recording device comprising a diaphragm-type support

ABSTRACT

The invention concerns a data recording device comprising a two-dimensional array of microtips ( 3 ), whereof the apex is generally of nanometric dimensions arranged opposite a storage medium consisting of a flexible diaphragm ( 2 ) borne by a frame ( 1 ) forming a plurality of cells. At least one microtip ( 3 ) is associated with each cell. Said device enables the dispersion in the height of the microtip to be compensated. In order to eliminate edge effects, the flexible diaphragm ( 2 ) may include first and second elementary diaphragms, separated by a network of spacer elements, laterally offset relative to the frame. In an alternative embodiment, an array of flexible plates, separated from the diaphragm by a two-dimensional array of spacer studs, may be used for subdividing each large-size cell into a plurality of elementary cells, each associated with at least one microtip.

BACKGROUND OF THE INVENTION

The invention relates to a data recording device comprising atwo-dimensional array of microtips, the apex whereof is generally ofnanometric dimensions, arranged in a plane facing a storage medium, andelectronic means for addressing and controlling the microtips so as toenable data recording on the storage medium.

STATE OF THE ART

Data recording, both in the computing field and in the multimedia field,has to meet an increasing need for capacity. Different techniques havebeen developed ranging from the magnetic hard disk to the DVD usingoptics and phase change materials. Whatever the recording techniqueused, it is always sought to reduce the size of the memory points (bits)and increasing the recording capacity means increasing the storagedensity.

Recently, very large storage capacities, of about a Terabit/cm², havebeen obtained by implementing micro-tips of the type used in the tipeffect microscopy field (“The Millipede—More than one thousand tips forfuture AFM data storage”, P. Vettiger et al., IBM J. RES. Develop., Vol.44, n^(o)3, May 2000, p. 323-340 and “Fabrication of microprobe arraywith sub-100 nm nano-heater for nanometric thermal imaging and datastorage”, Dong-Weon Lee et al., Technical Digest, MEMS 2001, 14^(th)IEEE International Conference on Micro Electro Mechanical Systems (Cat.N^(o)01CH37090), IEEE, Piscataway, N.J., USA, 2001, p. 204-207). Highdensity is obtained by localizing the bits by means of micro-tips theapex whereof is of nanometric dimension. The micro-tips are preferablyarranged in an array, with a parallel access to the data, which enablesexcellent performances to be achieved as far as rate is concerned. Asingle actuator, which may be electromechanical, enables a relativemonolithic movement of the whole of the array of micro-tips with respectto the surface of the storage medium.

In such a data recording device, with tip effect, it is necessary toguarantee a perfect contact of all the tips with the storage medium. Forreasons of complexity of the system, it is not envisageable to controlthe position of each microtip individually. However, the microtips arefabricated in collective manner, by techniques derived from those ofmicroelectronics, and a dispersion of the height of the microtips alwaysremains due to fabrication. Although this dispersion is very small,typically about 100 nm, the longest of the microtips of an array pressesmore than the others on the storage medium.

To overcome this difficulty, each microtip is borne overhanging by oneend of a cantilever, in similar manner to the microtip arrays used inlocal probe microscopy. The flexibility of the cantilever then enablesthe strain of a bearing to be absorbed.

However, the bearing forces of the microtips on the storage medium mustnot exceed a value of about 100 nN, so as not to damage the storagemedium. Indeed, as the contact surface of a microtip with the storagemedium is minute, the pressure is high. The cantilevers therefore haveto be very flexible to absorb the height dispersion of the microtips.For example, cantilevers having a stiffness of about 1 N/m, a length of100 μm, a width of a few tens of μm and a thickness of a few μm havebeen developed. It is difficult to envisage more flexible cantilevers.Their dimensions are in fact difficult to master due to their largelength in comparison with their small width and/or thickness. Inaddition, the positioning precision of the tips facing the surface ofthe storage medium would be adversely affected, thus limiting the memorydensity.

OBJECT OF THE INVENTION

The object of the invention is to achieve a data recording device notpresenting the above shortcomings and more particularly enabling theheightwise dispersion of the microtips to be ignored.

According to the invention, this object is achieved by the fact that thestorage medium comprises a flexible diaphragm borne by a frame forming aplurality of cells, at least one microtip being associated with eachcell. This frame enables a rigidity of the diaphragm to be ensured whileensuring it a freedom of movement inside each cell.

According to a development of the invention, two arrays of microtips arearranged on each side of the storage medium.

The two arrays of microtips are preferably laterally offset so that themicrotips associated with any one cell of the frame are not arrangedexactly opposite one another.

According to a preferred embodiment, the flexible diaphragm comprises atleast a first layer, performing the function of a memory, and a secondlayer designed to ensure a certain rigidity.

According to another development of the invention, the flexiblediaphragm comprises first and second elementary diaphragms separated byan array of spacer elements laterally offset with respect to the frame.This enables undesirable edge effects to be eliminated.

In another alternative embodiment, also enabling edge effects to belimited, the device comprises an array of flexible plates, separatedfrom the diaphragm by a two-dimensional array of spacer studs andsub-dividing each cell into a plurality of elementary cells eachassociated with at least one microtip.

The device preferably comprises means for relative movement of thestorage medium and of the microtip array in parallel to, and possiblyperpendicularly to said plane.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features will become more clearly apparent from thefollowing description of particular embodiments of the invention givenas non-restrictive examples only and represented in the accompanyingdrawings, in which:

FIG. 1 illustrates, in cross-section, a basic element of a deviceaccording to the invention.

FIG. 2 represents, in perspective, a particular embodiment of a supportframe of a diaphragm of a basic element according to FIG. 1.

FIG. 3 represents, in cross-section, two adjacent cells of a deviceaccording to the invention.

FIGS. 4 and 5 represent, in front view, two alternative embodiments of adevice according to the invention.

FIG. 6 represents, in cross-section, a device with a double array ofmicrotips.

FIGS. 7 and 8 represent, in cross-section, two successive fabricationsteps of the frame and of a part of the diaphragm of a device accordingto the invention.

FIG. 9 illustrates, in cross-section, an alternative embodiment of FIG.1.

FIG. 10 represents another particular embodiment of a device accordingto the invention.

FIGS. 11 and 12 illustrate respective positions of different elements oftwo alternative embodiments of the device according to FIG. 10.

FIG. 13 represents another particular embodiment of a device accordingto the invention.

FIG. 14 illustrates the respective positions of different elements of analternative embodiment of the device according to FIG. 13.

FIGS. 15 to 18 represent the successive steps of a process for achievinga device according to FIGS. 13 and 14.

DESCRIPTION OF PARTICULAR EMBODIMENTS

As represented in FIG. 1, a basic element of the data recording devicecomprises a frame 1 bearing, on one of its faces, a flexible diaphragm 2constituting the storage medium. Each basic element forms a cellassociated with a microtip 3 formed on a base 4 arranged facing thestorage medium, parallel to the latter.

A data recording device comprises a plurality of adjacent cellsassociated with a two-dimensional array of microtips (FIGS. 3 to 5).FIGS. 4 and 5 illustrate two particular configurations able to be used,with cells respectively of rectangular shape (FIGS. 2 and 4) and ofhexagonal shape (FIG. 5).

In the rest position, the microtips 3 can be either in contact with theflexible diaphragm 2 or withdrawn with respect to the latter. In thelatter case, in the read or write position, the storage medium is movedperpendicularly to the base 4 so as to bring the microtips 3 intocontact with the storage medium formed by the flexible diaphragm 2. Therelative movement of the storage medium and of the microtipsperpendicularly to their plane is preferably achieved by movement of thesupport frame 1 of the diaphragm, the base 4 on which the microtips 3are formed remaining fixed.

A relative movement of the microtips 3 and of the storage medium, in adirection parallel to the plane of the flexible diaphragm, with orwithout contact with the latter, can also be communicated to thediaphragm and/or to the microtips by actuators (not shown), themselvescontrolled by a microcomputer.

Control and addressing or multiplexing of the microtips 3 in the read orwrite position is performed by any suitable means, preferably by anelectronic circuit achieved by means of integrated technology in thebase 4. The microtips 3, which are fixed, can then be achieved bymicroelectronics techniques on silicon. The whole surface of the base 4situated facing the storage medium is in fact available for theelectronic addressing and control circuit of the microtips, which doesnot have to be removed to the end of the memory as in a number of priorart devices. This enables the silicon surface used to be optimized. Inthe case of an electrical memory, a current has to flow from themicrotips to the electrically conducting diaphragm, the latter thenbeing connected by an electrical connection (not shown) to theelectronic circuit arranged in the base 4.

The flexible diaphragm 2 is formed by a layer with an extremely smallthickness, from about a few nanometers to a few micrometers, which canbe conducting. It therefore deforms under the action of a local forceperpendicular to its surface. For example, it can be shown that, underthe action of a centered force of 100 nN, a diamond-like carbon layerwith a thickness of 10 nm, tightened on a frame having dimensions (side,diameter, etc.) of about 100 μm, deforms with a sag of about 12 μm,which corresponds to an equivalent stiffness of only 8.3 nN/μm, i.e.more than two orders of magnitude less than that of conventionalcantilevers. It is easy to adjust this stiffness constant by choosing alayer with a more or less large thickness, the stiffness beingproportional to the cube of the thickness of the diaphragm.

This low value of the stiffness constant allows a large heightdispersion of the microtips 3 without resulting in large bearing forces.In the above example, a height variation of the microtip of 100 nm onlyrepresents a variation of the bearing force of 0.83 nN, i.e. less than1% of a nominal bearing of 100 nN. All the height dispersions of themicrotips due to the fabrication technologies then do not have anyinfluence in comparison with the amplitude of an imposed meandeformation of the diaphragm, i.e. 12 μm in the example above.

In FIGS. 4 and 5, the bearing points of the flexible diaphragm 2 of themicrotips 3 associated with each cell of the frame 1 are represented in5. These impact points are not arranged at the center of each of thecells but are off-center, the frame and diaphragm moving with respect tothe microtip array, parallel to the diaphragm plane, in the course ofread and/or write.

The flatness of the frame 1 must be compatible with the tolerance on thebearing force of the microtips 3, i.e. the same as the tolerance on theheight dispersion of the microtips, which can be relatively large, asindicated above. For the same reasons, it is not necessary to have anexceptional flatness of the storage medium.

The diaphragm 2 has a low stiffness in the dimension normal to itsplane, but it presents a large stiffness for tangential or lateraldeformations, unlike cantilever structures which suffer from a largelateral flexibility able to limit the memory density, even if they areoptimized with triangular shapes. This good geometric rigidity enables aprecise positioning of the end of the microtips with respect to thesurface of the diaphragm.

Unlike memories using a cantilever array, the size of the memory may belarge, i.e. greater than 1 cm², to provide a larger data recordingcapacity.

Due to the flexibility of the diaphragm 2, an actuator (not shown),which moves the frame 1 bearing the diaphragm 2 constituting the storagemedium, does not have to guarantee such a demanding precision as indevices using a cantilever array, in the dimension perpendicular to theplane of the diaphragm. A precision of about a few micrometers issufficient, whereas a precision of about a nanometer is necessary in theprior art. This tolerance simplifies the design of the actuatorenormously.

The device also presents a good tolerance as far as the roughness of thediaphragm 2 is concerned, the inherent flexibility of the latterenabling the roughnesses, deliberate or not, of the diaphragm to beabsorbed, for example those constituted by patterning of the latter orby lines.

The device according to the invention can have a high density ofmicrotips 3. Thus, in the prior art, the microtip arrays envisagedcomprise 100×100 elements, with a 100 μm pitch, the size of thecantilevers and the presence of the tip addressing lines fixing theminimum pitch. In the device according to the invention, the cells canbe much smaller (10 μm for example) due to the absence of cantileversand to the arrangement of the addressing circuit with respect to thestorage medium. It is thus possible to obtain memories with a highparallelism to reduce the access time thereof.

In the particular embodiment represented in FIG. 6, the memory capacityis doubled due to the use of the double-faced storage medium. The devicethen comprises two microtip arrays (3 a, 3 b) arranged on each side ofthe storage medium 2. The two microtip arrays 3 a and 3 b are preferablylaterally offset so that the microtips 3 a and 3 b associated with anyone cell of the frame are not located exactly facing one another.

In FIG. 6, the microtips 3 a of a first microtip array are in contactwith a face of the diaphragm 2 enabling read or write, under the controlof the corresponding electronic circuit integrated in the base 4 a,whereas the microtips 3 b of the second microtip array, in contact withthe opposite face of the diaphragm 2, enable read or write under thecontrol of the corresponding electronic circuit integrated in the base 4b. The frame 1 or the two microtip arrays, preferably fixedly secured toone another by a connection 11 joining the bases 4 a and 4 b, can bemoved in planes parallel to the plane of the diaphragm during the reador write operations under the control of the corresponding electroniccircuits integrated in the bases 4 a and 4 b.

In an alternative embodiment, the microtips 3 a of the first microtiparray are in contact with the diaphragm 2, enabling read or write underthe control of the corresponding electronic circuit integrated in thebase 4 a, whereas the microtips 3 b of the second microtip array are ata slight distance from the diaphragm. Movement of the diaphragm supportframe 1, perpendicularly to the plane of the diaphragm, in the directionof the second microtip array 3 b, causes the microtips 3 a of the firstarray to be moved away from the diaphragm, whereas the microtips 3 b ofthe second array come into contact with the diaphragm enabling read orwrite, under the control of the corresponding electronic circuitintegrated in the base 4 b. The distance between the bases 4 a and 4 bcan be chosen so that no microtip comes into contact with the diaphragmin a central rest position. Movement of the frame can be replaced by asimultaneous movement of the two microtip arrays, preferably secured toone another by their bases 4 a and 4 b (connection 11).

In another alternative embodiment, the bases 4 a and 4 b of the twomicrotip arrays are not secured to one another. They can be movedsimultaneously and in opposite directions with respect to the storagemedium. In a first, rest, position, the two bases 4 a and 4 b areseparated from the plane of the frame 1, and no microtip is in contactwith the diaphragm 2. In a second, read or write, position, the twobases 4 a and 4 b are moved in the direction of the storage medium andall the microtips 3 a and 3 b come into contact with the diaphragm, onboth sides of the latter. Read and write of each of the faces of thestorage medium are then, as in FIG. 6, controlled by the electroniccircuits respectively integrated in the bases 4 a and 4 b.

The electronic control and addressing circuit situated in the base 4 canbe achieved by means of any technology on silicon, the microtips 3 thenbeing achieved by a microelectronics technology on silicon. Themicrotips can, for example, be made from silicon, possibly covered witha conducting and/or hard material, for example titanium nitride (TiN),tungsten carbide (W₂C) or amorphous diamond-carbon (diamond-like carbon,possibly doped to be conducting), as described in the article “Procédésde fabrication de micropointes en silicium”, D. Moreau et al., Le Vide,n^(o) 282, October-December 96, p. 463-477, ISSN 1266-0167 or in thearticle “Novel probes for scanning probe microscopy”, E. Oestershulze,Applied Physics A 66, 1998, S3-S9.

To guarantee the absence of wear of the microtips, it is alsoenvisageable to make them from solid diamond according to the processdescribed in the article “Fabrication of monolithic probes for scanningprobe microscopy applications”, C. Mihalcea et al., Applied Physics A66, 1998, S87-S90.

The storage medium is formed by a stack of layers constituting theflexible diaphragm 2. The stack of layers mainly comprises two layers, afirst layer acting as memory and a second layer, called the mechanicallayer, designed to provide the flexible diaphragm with a certainrigidity. The first layer, performing the function of memory, is made ofa material dependent on the envisaged recording techniques, for examplea thermoplastic material, phase change material, magnetic material, etc.Other layers can perform thermal or electrical functions if required,certain layers being able to contribute simultaneously to severalfunctions.

FIGS. 7 and 8 illustrate two successive fabrication steps of a siliconframe 1 and of the mechanical layer of the diaphragm borne by the frame1. In a first step (FIG. 7), the mechanical layer 6 is deposited on asilicon layer 7 with a thickness of 100 to 500 μm, oriented (100). Themechanical layer 6 is for example formed by an amorphous carbon ordiamond-like carbon (DLC) coating deposited on the silicon layer 7 byany known process, for example by chemical vapor deposition (CVD) orphysical vapor deposition (PVD). The patterns of the cells are thenachieved by photo-resist on the face of the silicon layer 7 opposite themechanical layer 6 so as to form a resin mask 8.

The silicon layer 7 is then chemically etched, for example by potassiumhydroxide (KOH) etching through the resin mask 8. Etching, performedaccording to preferred crystalline planes (111), is selective and stopson the mechanical layer 6 of the diaphragm. The remaining part of thesilicon layer thus forms the frame 1 in which the cells are formed, thebottom whereof is constituted by the mechanical layer 6 of the diaphragmthus borne by the frame.

In the particular embodiment illustrated in FIG. 8, a residual layer ofsilicon is kept, in contact with the mechanical layer 6 of thediaphragm. This residual layer of silicon 9 enables the rigidity of thediaphragm to be increased or a specific mechanical contact to beachieved.

The other layers of the diaphragm, layer performing the function ofmemory and complementary packaging layers, can then be achieved on themechanical layer 6. These layers could possibly be achieved beforeetching of the silicon layer 7. In this case, it is neverthelessnecessary to protect them from the chemical etching, for example bymeans of an enclosure fixed tightly on the silicon layer 7.

In the alternative embodiment represented in FIG. 9, the first andsecond layers of the diaphragm (layer 10 performing the function ofmemory and mechanical layer 6) are represented, the microtip 3 cominginto contact with the mechanical layer 6. This can enable, in certaincases, a significant bearing force to be had between the microtip andthe storage medium, without however exerting any stress on the layer 10performing the function of memory. Such a bearing force can proveinteresting in particular in the case of electrical recording on a phasechange material. The thickness of the mechanical layer 6 makes itpossible to determine the force applicable without stressing the layer10 performing the function of memory, deposited on the face of themechanical layer opposite the face of the diaphragm in contact with themicrotips 3.

The device according to the invention thus enables a choice to be madebetween a weak bearing force and a higher bearing force, according tothe recording techniques used, which is not possible with a device usingcantilevers.

In the above-described recording device, an edge effect may occur when amicrotip 3 bears on the flexible diaphragm 2 near to the frame 1. Ineach cell, the flexibility of the storage medium in fact decreases fromthe center to the edge of the flexible diaphragm. It is possible tolimit this effect by limiting the scanned surface to a fraction of thesurface of the diaphragm of each cell. Such a limiting is however notoptimal in terms of use of the storage medium.

The particular embodiment represented in FIG. 10 enables this edgeeffect problem to be solved. In this device, the flexible diaphragmcomprises a first elementary diaphragm 2 a associated with the frame 1as in FIG. 1, and a second elementary diaphragm 2 b. The two elementarydiaphragms 2 a and 2 b are separated by an array of spacer elements 12,which is offset with respect to the frame 1. The array of spacerelements can be formed by a plurality of individual spacer studs 12 a(FIG. 11) or form an intermediate frame 12 b (FIG. 12). The spacerelements 12 have a sufficient thickness to prevent contact between thetwo elementary diaphragms when deformation thereof takes place.

Thus, when a microtip 3 moves towards the frame bounding the edge of acell, only the second elementary diaphragm 2 b deforms and the bearingforce remains low. When the microtip 3 comes to bear against the secondelementary diaphragm 2 b at the level of a spacer element 12, thedeformation is transmitted to the first elementary diaphragm 2 a at alocation situated away from the frame 1 and consequently presenting asufficient flexibility. In all cases, at least one of the elementarydiaphragms ensures the flexibility sought for and compensates any heightdispersion of the microtips. Thus, it is possible to eliminate any edgeeffect by using a double diaphragm with nested frames, formed by addingthe second elementary diaphragm 2 b, which is connected to the firstelementary diaphragm 2 a by spacer elements 12, only at locationslaterally offset with respect to the frame.

This double diaphragm (2 a, 12, 2 b) can be achieved from a stackingcomprising an alternation of silicon layers, designed to form the frame1 and the spacer elements 12, and of thin layers of material of the typedescribed above, designed to form the elementary diaphragms 2 a and 2 b.Such a stacking can be obtained by successive cuttings and stickings ofsilicon wafers by any known process, in particular by a process of theSmart Cut® type. The silicon can be removed by chemical etching by aprocess comparable with that described with reference to FIGS. 7 and 8for fabrication of a single diaphragm. For this, openings are made inthe first diaphragm 2 a, by photo-masking, to enable isotropic etching,by chemical means, of the silicon layer designed to form the spacerelements 12. The first diaphragm 2 a is then partially perforated.

Another particular embodiment, illustrated in FIGS. 13 and 14, enablesthe edge effect caused when a microtip 3 bears on the flexible diaphragm2 near to the frame 1 to be reduced. An array of thin flexible plates13, separated from the diaphragm 2 by a two-dimensional array of spacerstuds 12 a, subdivides each cell into a plurality of elementary cellseach associated with at least one microtip. Each cell can then have muchlarger dimensions than the pitch P1 of the microtip array (typicallyless than 100 μm) and its sides can measure for example up to 1 cm. InFIGS. 13 and 14, a substantially square cell bounded by the frame 1 issubdivided into 16 elementary cells by two perpendicular, criss-crossedseries of three parallel plates 13. In practice, the number of microtipsof the array being about ten thousand, the number of elementarydiaphragms subdividing a cell can for example be about one hundred(10×10). The thickness of the plates 13 is much smaller than thethickness of the frame 1 (from 100 μm to 500 μm) so as to ensure a largeflexibility of the storage medium inside each cell of large dimensions.The edge effect mentioned above can therefore only occur near to theframe 1, i.e. for a very limited number of microtips 3.

The flexibility of the plates 13 is a function of the cube of theirthickness and proportional to their width. It also depends on theirlength between two fixed points, i.e. on their length between two spacerstuds 12 a. The latter dimension is a function of the pitch P1 of themicrotip array. To enhance the flexibility of the plates 13, it ispossible to associate several microtips with each elementary cell. Theflexibility of the assembly can also be enhanced by choosing, for thearray of spacer studs, a slightly different pitch P2 from the pitch P1of the microtip array, preferably in the two dimensions of the storagemedium plane, as represented in FIGS. 13 and 14. In this case, when amicrotip 3 is situated facing a spacer stud 12 a, the closest microtipsare offset with respect to the adjacent spacer studs. It is then theflexibility proper to the diaphragm 2 which absorbs the heightdifferences of the microtips 3.

According to the fabrication process of a device with plates accordingto FIGS. 13 and 14 illustrated in FIGS. 15 to 18, the frame 1 and plates13 are formed in a single layer 14 of silicon, from 100 μm to 500 μmthick, located on a silicon dioxide layer 15 having a thickness of 50 nmto 500 nm, designed for formation of the spacer studs 12 a, itselfdeposited on the diaphragm 2. This layer 15 can also be made of siliconnitride or of carbon.

In a first step, illustrated in FIGS. 15 and 16, the silicon layer 14 isetched anisotropically through a mask 16 protecting the location of theframe 1 and plates 13. In a second step, illustrated in FIG. 17, theplates 13 are thinned by selective isotropic etching of the siliconlayer 14 through a mask 17 protecting the frame 1 only. In a last step,represented in FIG. 18, the spacer studs 12 a are disengaged byselective isotropic etching of the layer 15 through a mask (not shown),the zones whereof situated facing the spacer studs have been enlargedwith respect to the corresponding zones of the mask 16 of FIG. 15 usedin the course of the first step. This makes it possible to prevent anoveretching effect, which would reduce the formation of the islandsconstituted by the spacer studs 12 a.

As in the previous embodiments, the diaphragm 2 can for example beformed by stacking of a mechanically rigid layer, for example made ofamorphous diamond-like carbon (DLC) and a layer performing the memoryfunction (plastic, phase change material, . . . ). The latter layer maybe deposited after the third step of FIG. 18, the initial stacking ofFIG. 15 then only comprising the rigid mechanical layer, for examplewith a thickness of 100 nm, of the diaphragm.

The invention is not limited to the particular embodiments describedabove. In particular the flexible diaphragm 2 can comprise a layer madefrom diamond-like carbon, silicon, silicon oxide (SiO₂) or even metal.If electrical conduction of the diaphragm 2 is required, the mechanicallayer 6 of the diaphragm 2 can be doped, for example by boron or silver.

1. Data recording device comprising: a two-dimensional array ofmicrotips attached directly to a fixed, rigid base and arranged in aplane opposite a storage medium, and electronic means for addressing andcontrolling the microtips so as to enable data recording on the storagemedium, the storage medium comprising a flexible diaphragm borne by aframe laterally, delimiting a plurality of cells, at least one micro-tipbeing associated with each cell, the flexible diaphragm comprises twofree faces parallel to the plane.
 2. Device according to claim 1,wherein the microtips have an apex of nanometric dimensions.
 3. Deviceaccording to claim 1, wherein the cells are rectangular.
 4. Deviceaccording to claim 1, wherein the cells are hexagonal.
 5. Deviceaccording to claim 1, comprising two arrays of microtips arranged oneach side of the storage medium.
 6. Device according to claim 5, whereinthe two arrays of microtips are laterally offset so that the microtipsassociated with any one cell of the frame are not arranged exactlyopposite one another.
 7. Device according to claim 1, wherein the frameis formed by a silicon layer in which the cells are formed.
 8. Deviceaccording to claim 1, wherein the flexible diaphragm comprises at leasta first layer, performing the function of a memory, and a second layerdesigned to ensure a certain rigidity.
 9. Device according to claim 8,wherein the second layer is an amorphous carbon or diamond-like carbonlayer deposited on a silicon layer before formation of the cells isperformed on the opposite face of the silicon layer.
 10. Deviceaccording to claim 9, wherein the second layer is doped by boron orsilver.
 11. Device according to claim 1, wherein the flexible diaphragmcomprises first and second elementary diaphragms separated by an arrayof spacer elements laterally offset with respect to the frame. 12.Device according to claim 11, wherein the array of spacer elementsconstitutes an intermediate frame.
 13. Device according to claim 12,wherein the spacer elements are formed by studs.
 14. Device according toclaim 1, comprising an array of flexible plates, separated from thediaphragm by a two-dimensional array of spacer studs and sub-dividingeach cell into a plurality of elementary cells each associated with atleast one microtip.
 15. Device according to claim 14, wherein the numberof microtips of the array being about ten thousand, the number ofelementary cells subdividing a cell is about one hundred.
 16. Deviceaccording to claim 14, wherein the array of microtips has a slightlydifferent pitch from that of the array of spacer studs.
 17. Deviceaccording to claim 14, wherein the frame and plates are formed in asilicon layer having a thickness of 100 μm to 500 μm.
 18. Deviceaccording to claim 11, wherein the spacer elements or studs are made ofsilicon dioxide, silicon nitride or carbon, with a thickness of 50 nm to500 nm.
 19. Device according to claim 1, comprising means for relativemovement of the storage medium and of the microtip array, in a directionparallel to said plane.